Technical Field
The present application generally relates to lithium ion batteries and, more particularly, relates to a lithium ion battery and a lithium ion battery pack having desirable safety performance.
Description of Related Art
At present, lithium ion batteries are becoming increasingly popular in electric vehicles and electricity grid energy storage equipment. Due to various kinds of safety accidents relating to lithium ion batteries, more and more attention has been paid to the safety performance of the lithium ion batteries in recent years.
Safety accidents of lithium ion batteries are generally caused by thermal runaway. Due to the raise of temperature, various reactions occur in a lithium ion battery, such as decomposition of SEI, reduction reaction between the positive electrode and the electrolyte, oxidation reaction between the negative electrode and the electrolyte, and evaporation and decomposition of the electrolyte. Various kinds of reactions will induce continuous raise of temperature and generation of massive gases in the lithium ion battery, which may lead to sharp raise of pressure in the lithium ion battery.
To avoid explosion of lithium ion battery due to sharp pressure increase, a lithium ion battery is equipped with a pressure relief valve. When the lithium ion battery is charged improperly, or short circuited or exposed to high temperature, the pressure in the lithium ion battery will increase sharply and the pressure relief valve will break to release the pressure, so as to improve the safety performance of the lithium ion battery.
However, a conventional lithium ion battery has the following shortages. When thermal runaway occurs, the temperature in the lithium ion battery is generally higher than 400° C. At this temperature, active materials in the positive electrode and the negative electrode will react with the electrolyte and massive gases are generated, including combustible gases and non-combustible gases. At the same time, combustible electrolyte vapor is also generated. Mixture of the gases and the vapor carrying the high temperature solid particles will spurt out rapidly via the pressure relief valve. The mixture of the combustible gases, the combustible electrolyte vapor and the high temperature solid particles will ignite in the surrounding air, which may eventually lead to the ignition of the lithium ion battery.
The prior art also discloses a lithium ion battery pack. The lithium ion battery pack includes at least one lithium ion battery and a housing for receiving the at least one lithium ion battery. The housing defines a vent hole for communicating the inner side and the outer side of the lithium ion battery. The vent hole is coupled with a metal mesh. When the flame carrying the high temperature materials and the gases spurts out, heat of the flame and the high temperature materials is absorbed by the metal mesh quickly. The gases or the combustible materials are discharged out of the lithium ion battery pack. The flame will not be vented onto the outside of the housing.
The lithium ion battery pack as previously discussed is generally used in portable electronic devices. Each lithium ion battery in the lithium ion battery pack generally has low capacity and low charge and discharge power. However, a lithium ion battery used in electronic vehicles and electrical grid energy storage equipment generally has much higher capacity and higher charge and discharge power than that of a lithium ion battery used in portable electronic devices. When thermal runaway occurs, the heat generated by a lithium ion battery used in electronic vehicles and electrical grid energy storage equipment is much more than the heat generated by a lithium ion battery used in portable electronic devices, which will inevitably lead to the following disadvantages.
Firstly, the chamber between the housing and the lithium ion batteries is in communication with the surrounding air via the vent hole coupled with the metal mesh. There is also air in the chamber. When thermal runaway occurs to the lithium ion battery, the flammable materials and high temperature materials spurted out from the lithium ion battery will mix with the air in the chamber. The combustible gases will be ignited and burn vigorously in the confined space of the chamber, which will adversely affect the safety performance of the lithium ion battery.
Secondly, the housing is arranged at outside of the lithium ion batteries. When thermal runaway occurs to one of the lithium ion batteries, especially occurs to a lithium ion battery afar from the vent hole, the materials spurted out may pollute other lithium ion batteries in the same lithium ion battery pack or the circuit for connecting the lithium ion batteries, and further induce thermal runaway of all of the lithium ion batteries in the lithium ion battery pack. In addition, the housing will hinder the heat exchange between the lithium ion batteries and the surrounding air and lead to heat accumulation, which will adversely affect the safety performance of the lithium ion battery pack.
Thirdly, although the metal mesh covering the vent hole can prevent the flame from spraying onto the outside of the housing, the metal mesh can absorb and dissipate only portion of the heat. For a lithium ion battery which may generate a large amount of heat used in electronic vehicles, if the heat which fails to be dissipated by the metal mesh accumulates continuously, the flame may pass through the metal mesh and continue to burn.
In view of the foregoing, what is needed, therefore, is to provide a lithium ion battery and a lithium ion battery pack which has desirable safety performance.